The present invention relates to an electron beam exposure apparatus and, more particularly, to an electron beam exposure apparatus which can quickly and precisely measure and correct any position variation of an electron beam with respect to a stage that carries an object to be exposed, and a device manufacturing method using the same.
In an electron beam exposure apparatus, the position stability of an electron beam with respect to a stage that carries the object to be exposed is an important factor that determines its work precision. As factors that impair the position stability of an electron beam, an electron beam position variation resulting from charging of a contaminant such as a carbon compound that has become attached inside an electron optical system, and an electron beam position variation arising from a thermal or mechanical deformation of a structure for supporting the electron optical system, the stage, and an interferometer that detects the stage position are known. When the electron beam position has varied, the relationship between the writing coordinate position defined by the electron beam and the coordinate position of the stage defined by the interferometer deviates before or after writing, or during writing, thus impairing the stitching precision and overwriting precision of the patterns to be written.
Conventionally, a displacement between the writing coordinate system and stage coordinate system due to an electron beam position variation is corrected by the following method.
A reference mark is formed on a movable stage which carries a sample such as a wafer or the like. The stage is then moved on the basis of a stage coordinate system defined by the interferometer to locate the reference mark at the design standard irradiation position of an electron beam, and a mark coordinate position (X0, Y0) of the reference mark is obtained by the electron beam. Writing is temporarily stopped during writing, and the stage is moved again to locate the reference mark at the standard irradiation position of the electron beam. The coordinate position of the standard position is detected by the electron beam to obtain a mark coordinate position (X1, Y1) at that time. A difference (xcex94X1, xcex94Y1) between the previous mark coordinate position (X0, Y0) and the current mark coordinate position (X1, Y1) is calculated to obtain the electron beam position variation. Then, the deflection position of the electron beam or stage position is corrected based on this difference (xcex94X1, xcex94Y1). The aforementioned operation is repeated until the end of writing.
However, when the required stitching precision or overwriting precision becomes stricter, the allowable range of electron beam position variations becomes narrower, and electron beam position variations must be corrected more frequently. As a result, a problem, i.e., low throughput of the electron beam exposure apparatus, remains unsolved.
It is an object of the present invention to provide an excellent electron beam exposure apparatus which can solve the above problems, and a device manufacturing method.
It is another object of the present invention to allow quick correction of the positional relationship between the stage and electron beam upon writing a pattern on a substrate by the electron beam, and to attain both high writing precision and high throughput.
According to one aspect of the present invention, there is provided an electron beam exposure apparatus comprising: a stage which moves while carrying a substrate; a first reference mark fixed onto the stage; an electron optical system for writing a pattern to be written by deflecting an electron beam on the substrate by deflection means, irradiating an object to be irradiated on the stage with the electron beam, detecting electrons reflected by the object, and detecting a position of the object with respect to the electron beam; a second reference mark fixed to the electron optical system and located in a deflection range of the electron beam; a distance measurement system for detecting a position of the stage; and control means for detecting a position of the first reference mark using the electron optical system, detecting the position of the stage at that time using the distance measurement system to obtain a positional relationship of the stage with respect to the electron beam, pre-detecting a position of the second reference mark using the electron optical system, detecting the position of the second reference mark again using the electron optical system upon writing a pattern to be written on the substrate by the electron beam by making the stage and the deflection means cooperate with each other on the basis of the obtained positional relationship between the electron beam and the stage, calculating a difference between the currently detected position and the pre-detected position of the second reference mark, and correcting a relative position between the electron beam and stage using at least one of the deflection means and the stage on the basis of the calculated difference.
Preferably, the control means detects the position of the second reference mark using the electron optical system during writing of the pattern to be written on the substrate by the electron beam, calculates the currently detected position and the pre-detected position of the second reference mark, and corrects the relative position between the electron beam and stage using at least one of the deflection means and the stage on the basis of the calculated difference.
Preferably, the distance measurement system detects the position of the stage relative to the electron optical system.
Preferably, the distance measurement system has a movable mirror fixed to the stage, a reference mirror fixed to a position detection system, and means for irradiating the movable mirror and reference mirror with a laser beam, bringing laser beams reflected by the movable mirror and reference mirror to interference, and detecting that interference light.
According to another aspect of the present invention, there is provided an electron beam exposure method for writing a pattern to be written on a substrate, which is placed on a stage, with an electron beam coming from an electron optical system, comprising the step of detecting a position of a first reference mark fixed to the stage using the electron beam, detecting a position of the stage at that time using a distance measurement system to obtain a positional relationship of the stage with respect to the electron beam, and pre-detecting a position of a second reference mark, which is fixed to the electron optical system and is located in a deflection range of the electron beam, using the electron beam; and the step of detecting the position of the second reference mark again using the electron beam upon writing the pattern to be written on the substrate using the electron beam on the basis of the obtained positional relationship between the electron beam and the stage, calculating a difference between the currently detected position and the pre-detected position of the second reference mark, and correcting a relative position between the electron beam and the stage on the basis of the calculated difference.
The electron beam exposure method preferably further comprises the step of detecting the position of the second reference mark using the electron beam during writing of the pattern to be written on the substrate using the electron beam, calculating the difference between the currently detected position and the pre-detected position of the second reference mark, and correcting the relative position between the electron beam and the stage on the basis of the calculated difference.
Preferably, the distance measurement system detects the position of the stage relative to the electron optical system.
Preferably, the distance measurement system irradiates a movable mirror fixed to the stage and a reference mirror fixed to the electron optical system with a laser beam, brings laser beams reflected by the movable mirror and reference mirror to interference, and detects that interference light.
According to still another aspect of the present invention, there is provided a device manufacturing method for manufacturing a device using the aforementioned electron beam exposure apparatus or method.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.